PowerShell Base64 Encoded IEX Cmdlet

Severity: high
Author: Florian Roth (Nextron Systems)
Source: upstream

Detects usage of a base64 encoded "IEX" cmdlet in a process command line

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation
Security-Auditing	4688	A new process has been created.

Stages and Predicates

Stage 1: `selection`

or:
CommandLine|contains: 'IEX (New'
CommandLine|contains: 'IEX (['
CommandLine|contains: 'IEX(('''
CommandLine|contains: 'IEX(New'
CommandLine|contains: 'IEX(['
CommandLine|contains: JAEUAWAAgACgATgBlAHcA
CommandLine|contains: JAEUAWAAgACgAWw
CommandLine|contains: SQBFAFgAIAAoAE4AZQB3A
CommandLine|contains: SQBFAFgAIAAoAFsA
CommandLine|contains: aQBlAHgAIAAoAE4AZQB3A
CommandLine|contains: aQBlAHgAIAAoAFsA
CommandLine|contains: 'iex (New'
CommandLine|contains: 'iex (['
CommandLine|contains: 'iex(('''
CommandLine|contains: 'iex(New'
CommandLine|contains: 'iex(['
CommandLine|contains: kARQBYACAAKABOAGUAdw
CommandLine|contains: kARQBYACAAKABbA
CommandLine|contains: kAZQB4ACAAKABOAGUAdw
CommandLine|contains: kAZQB4ACAAKABbA
CommandLine|contains: pAGUAeAAgACgATgBlAHcA
CommandLine|contains: pAGUAeAAgACgAWw

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.